In previous applications, filter modules have been used in a variety of applications and fluidic environments. When in service, it is often desirable to sense various fluid flow and filter performance characteristics in order to determine whether a filter element within the filter module is performing within application specifications and whether a filter element must be replaced or reconditioned before continuing operation.
In typical filter modules, a filter element is encased within a filter body and between inlet and outlet end caps. A filter manifold(s) may be attached to the filter body to feed unfiltered medium to the upstream side of the filter element (e.g., where the filter element is cylindrical, the outside of the filter element). As the medium passes to the downstream side of the filter element through the membrane material, contaminants are removed from the medium. Filtered medium is then collected from the downstream side of the filter element (e.g., where the filter element is cylindrical, the inside of the filter element).
During the filter element's service life, an increasing amount of removed contaminant will collect on one side of the filter element in a phenomenon known as fouling. Fouling causes the pressure difference between the upstream and downstream sides of the filter element to increase and thereby lowers the filtration efficiency of the filter element. If the differential pressure exceeds a certain value that is dependent upon the filter element material and design, the filter element may be damaged. Additionally, at high differential pressures, particle breakthrough (i.e., contaminant particles passing through the pores in the filter element) may occur.
In prior modules, the filter head may have contained conventional pressure transducers, differential pressure sensors, virtual pressure switches and temperature detectors to measure characteristics of fluid flow and filter performance. These components were used to sense the pressure differential across the filter element to determine whether the filter element was sufficiently clogged with contaminant removed from the fluid flow to require replacement. These pressure sensors were generally binary in nature, i.e., they either indicated that the filter element needed to be replaced (e.g., by causing a part to pop up out of exterior of the filter head) or that it was still useable.
The use of the pressure-sensing components used in traditional filter modules is often a significant design constraint in weight- and size-sensitive applications, e.g., aircraft filtration systems. Moreover, traditional filter modules offer no means for predicting when a filter element will need to be replaced. Finally, traditional filter modules disturb or alter fluid flow by requiring that pressure-sensing components be inserted into the stream of flow, creating turbulence.